In his new book, "My Father at 100" (Viking), Ron Reagan - the youngest son of former President Ronald Reagan - claims his father exhibited signs of Alzheimer's three years into his first term.
Doctors diagnosed Mr. Reagan with the memory-robbing disease five years after he left office, notes CBS News senior White House correspondent Bill Plante.
"Knowing what we know now, about the nature of Alzheimer's disease, we know that, decades before symptoms begin arriving, changes are happening in the brain," Ron Reagan writes.
He said he was alarmed by his father's performance in his Oct. 7, 1984 presidential debate with Democratic challenger Walter Mondale. He writes of that day, "My heart sank as he floundered his way through his responses, fumbling with his notes, uncharacteristically lost for words. He looked tired and bewildered."
Nancy Reagan has not publicly commented on the claim made by her son, but the former president's eldest son, Michael Reagan, did. On Saturday he sent a message on Twitter reading, "Ron, my brother was an embarrassment to his father when he was alive and today he became an embarrassment to his mother."
Reagan, author of the new book "The New Reagan Revolution: How Ronald Reagan's Principles Can Restore America's Greatness" (Macmillan), admitted today that it was a strong statement but that "it needed to be a strong statement."
On CBS' "The Early Show" this morning, Reagan, a political consultant for the Reagan Group, said, "All these years I've listened to people like Bill Maher and other people on the left who inferred my father had Alzheimer's when he was President of the United States to somehow discount the great job my father did as president.
"So now for one of his sons to come out and in fact say, 'Yeah, he might have had Alzheimer's or he had Alzheimer's during that time,' just gives credence to people like Bill Maher and others. It absolutely offends me that somebody would say that when there's no evidence anywhere on the planet to back it up," he told anchor Erica Hill.
"Your brother has said this is just his own feeling, no one else is saying it to him," Hill said. "He also doesn't think it would take away from your father's legacy at all if, in fact, that had been the case. You seem to differ on that - you feel that it would have an effect on his legacy. Could it be possible there may have been something else? Could he have had dementia?"
"No, he didn't have dementia," Reagan said. "Look what he accomplished in the last four years of his presidency: Reykjavik, S.T.A.R.T. agreements, all the things he accomplished. The speech at the Berlin Wall in 1987 on June 12th.
"Someone with dementia does not accomplish all of those things," he said.
Michael also believed it was "interesting" that Ron would infer his father suffered from Alzheimer's because, he said, the family didn't know if Ron voted for his father.
"This is the first time I heard he even watched the debate with Mondale," Michael said. "He might have voted for Mondale."
But when asked if that would have had any effect on whether or not Ronald Reagan had Alzheimer's, Michael said, "My father did not have dementia. The fact is, he was overloaded with facts and figures, everybody said that at the time. The next debate, he took Mondale to the cleaners on that one. And the rest is history. He won the biggest election in the history of mankind when he won in 1984."
While expressing clear resentment towards his brother, Michael spoke approvingly of those who speak warmly of his father, even those on the left.
He told the story of encountering Alec Baldwin at his California gym:
"I walk out of the gym one day and said, 'Alec, Mr. Baldwin, my name is Mike Reagan, Jane Wyman is my mother.' He looks at me, and I said, 'I thought if I said "Ronald Reagan was my dad" you'd deck me.'
He said, 'You're the only one who can say that." I said, 'You're absolutely right. I just want to tell you how much I enjoy '30 Rock' and all the things you do, I enjoy your acting.'"
"He said, 'Let me tell you something, and I want you to tell your family . . . I miss your father," Reagan continued. "He says, 'Yes, you know, I bleed liberal blue, but the reality of it is, I just realized lately how much I miss him. And I miss him because your father had a good soul, and what the world is missing is that good soul.'
"So it's not just Sarah Palin - As I write in my book, people like Alec Baldwin, who never liked my father, understood the great soul my father had."